Device for cooling en electric motor for a turbo-fan

Abstract: This invention relates to a device for cooling an electric motor for a turbo-fan unit. The motor has a shaft (16) which extends through the motor (10) and which supports a turbo-fan impeller (20) which is placed outside a shell (11) belonging to the motor. The turbo-fan impeller rotates with a speed above 50.000 rpm thereby creating a primary air flow which via an outlet (35) escapes from the turbo-fan unit. The turbo-fan unit (20) comprises means by means of which a secondary air flow is created which at least partly cools the electric motor and which from one or several cooling air inlets (28,30) separated from the primary air flow

Description: This invention relates to a device for cooling an electric motor for a turbo-fan unit the motor having a shaft supporting a turbo-fan impeller which is placed outside a shell of the motor and which rotates with a speed which is above 50.000 rpm thereby creating a primary air flow which escapes from the turbo-fan unit via an outlet. Units of the type described above are shown in WO 94/15518 and WO 94/15519 resp. and are because of its small dimensions suggested to be used as a vacuum source for vacuum cleaners in particular for hand held appliances. Cooling of the motor is in this case effected by directing the air flow from the turbo-fan unit outside the electric motor before the air escapes to atmosphere. It has however proved that this type of cooling - because of the concentrated heat emittance in the internal parts of the electric motor i.e. in bearings, rotor and stator - is not sufficient to get an acceptable lifetime of the electric motor. In order to improve the cooling effect it is of course possible to let the complete air flow or a part of the air flow created by the turbo-fan impeller pass the internal parts of the motor but this is not desirable because the air flow in certain applications is moisty and contaminated with particles and thus could damage the motor. It is also a risk that a blocking of the air flow which could occur for instance if the unit is used as a vacuum source in a vacuum cleaner,means that cooling does not occur and this could after a short period cause a motor breakdown. It is also previously known, see DE-A-3543833, to cool electric motors for ventilators by providing the motor with a seperate cooling air fan and surrounding the motor with a chamber which is connected to atmosphere so that air can be drawn outside the motor shell. The purpose of this invention is to achieve an effective cooling of the electric motor at said type of device the cooling being independent of the air flow through the turbo-fan unit. This is achieved by means of a device which has the caracteristics mentioned in the claims. Two embodiments of the invention will now be described with reference to the accompanying drawings in which Fig. 1 and 2 show a vertical section through a turbo-fan unit according to the two embodiments. With reference to Fig. 1 the turbo-fan unit comprises an electric motor 10 which is surrounded by a motor shell 11 with a first and a second end wall 12 and 13 resp. each having a hub part 14, 15 in which a shaft 16 is supported by means of bearings 17. The electric motor is electronically controlled and rotates at a speed which is above 50.000 rpm, preferably 70.000 - 120.000 rpm and has a stator 18 an a rotor 19 which is fixed to the shaft. The shaft 16 extends a short distance outside the first end wall 12 and supports a turbo-fan impeller 20 which is fixed at the shaft. The impeller has several fan blades 21 which with a very small play face a part 22 of an outer shell 23, the part 22 having a gradually increasing section area as seen in the flow direction, so that a turbo-fan unit,which forces the air through the unit, is created. The turbo-fan impeller is preferably shaped as an axial fan at the inlet side whereas the outlet side works as a radial fan. The outer shell 23 also forms a funnel shaped inlet 24 for the air flowing into the turbo-fan unit and has a cylindrical part 25 surrounding the motor shell 11 so that an annular shaped passage 26 is formed around the motor shell 11 this passage opening into a radially directed outlet 27. The second end wall 13 of the motor shell has several openings 28 placed about a hub part 15 these openings via an inlet part 29 communicating with an inlet opening 30 for cooling air. The first end wall 12 of the motor shell is in a corresponding way provided with outlet openings 31 for the cooling air and arranged around the hub part 14. The part of the turbo-fan impeller 20 facing the first end wall 12 forms a cooling air fan 32 and is preferably shaped as a radial fan with fan blades 33 for sucking the cooling air axially through the motor inside the shell 11. The fan blades, which have a small extension in the axial direction, with a very small play face the first end wall 12 which thus serves as a part of a fan housing. Hence, a cooling air outlet 34 is formed at the outer peripheral part of the cooling fan 32 this outlet 34 being situated near an outlet 35 belonging to the turbo-fan unit. The device operates in the following way. When the electric motor is running the shaft 16 rotates at a speed above 50.000 rpm thereby rotating the turbo-fan impeller 20 which means that air is drawn through the inlet 24 so that a primary air flow is created which flows through the outlet 35 of the turbo-fan unit and through the passage 26 before the air escapes via the outlet 27. At the same time cooling air is sucked in as a secondary air flow by means of the cooling air fan 32 from the inlet opening 30 via the openings 28 in the second end wall 13 into the electric motor and cools the bearings 17, the rotor 19 and the stator 18 before this air escapes via the openings 31 in the end wall 12 of the motor shell 12 to the central parts of the cooling air impeller 32. The secondary air then flows radially outwards from the cooling air fan via its outlets 34 and is mixed with the primary air flow in close vicinity of the outlet 35 of the turbo-fan unit. The device shown in Fig. 2 is mainly built up in the same way as the embodiment shown in Fig. 1 but differs with respect to the outlet arrangement from the turbo-fan unit 20 and the cooling fan 32. Thus an annular curved deflector plate 36 is fixed at the electric motor 10 or at the outer shell 23 and is placed at a distance from the motor shell 11 so that the secondary air flows between the deflector plate and the motor shell 11 whereas the primary air flows outside the deflektor plate. Thus, the primary air flow coming from the turbo fan impeller 20 is initially separated from the secondary air flow coming from the cooling fan 32 thereby giving the two flows the same flow direction before they merge. This arrangement has proved to give a considerable increase of the suction power of the turbo-fan unit. It should be mentioned that it is possible within the scope of the invention to use a mainly flat plate as a cooling air fan since the friction forces between the plate and the molecules in the air at the high speed beeing used are sufficient to get a radial flow over the surface thereby creating a cooling air flow through the motor.

Claims: Device for cooling an electric motor (10) for a turbo-fan unit the motor having bearings supporting a shaft (16) which is provided with a turbo-fan impeller (20) placed outside a first end wall (12) of a motor shell (11) and which rotates with a speed above 50.000 rpm thereby creating a primary air flow which escapes from the turbo-fan unit via an outlet (35), characterized in that the device comprises a cooling air fan (32) arranged at the same side of the motor shell as the turbo-fan impeller (20) and by means of which a secondary air flow is created which via one or several cooling air inlets (28,30), separated from the primary air flow, flows through the electric motor inside the motor shell (11) thereby passing the bearings, the rotor the stator and said end wall before leaving the shell via outlet openings (31) through said end wall. Device according claim 1 characterized in that the cooling air fan (33) is a radial fan. Device according to claim characterized in that the cooling air fan is a mainly flat plate. Device according to any of claims 1-3 characterized in that the turbo-fan impeller (20) and the cooling air fan (33) are integrated to one unit the turbo-fan impeller being one side of the unit whereas the other side facing the electric motor is the cooling air fan. Device according to any of the preceding claims, characterized in that the secondary air flow by means of a deflector plate is directed in mainly the same direction as the primary air flow before the flows merge.

Inventors: LINDMARK MAGNUS CARL WILHELM, MOREN LARS GUNNAR, WISS CHRISTER CALEB INGEMAR, LINDMARK, MAGNUS CARL WILHELM, MOREN, LARS GUNNAR, WISS, CHRISTER CALEB INGEMAR
Applicants: ELECTROLUX AB, AKTIEBOLAGET ELECTROLUX
Application year: 1994
Main classification: F04D25
IPC codes: F04D25, F04D29